1. Field of the Invention
Priority is claimed on Japanese Patent Application No. 2003-379873, filed Nov. 10, 2003, and Japanese Patent Application No. 2003-419479, filed Dec. 17, 2003, the contents of which are incorporated herein by reference.
The present invention relates to a squib (an ignition apparatus) which is used in a system which employs explosive, such as, for example, an air bag device or a pretensioner apparatus for an automobile, and particularly relates to a squib which incorporates an ignition element which can be ignited with low energy.
2. Background Art
Occupant protection apparatuses such as pretensioner apparatuses and airbag apparatuses that are mounted in automobiles operate by being ignited by a squib (i.e., an ignition apparatus) in which a gas generating agent is contained in an inflator, and high pressure gas that is generated by the combustion thereof is introduced into an airbag or the like.
A squib is constructed such that an igniting element is mounted on a header to which is fixed a connecting terminal in the form of a pin. In addition, an igniting agent in the form of an explosive is inserted under pressure into a cap so as to be in contact with the igniting element. The pin that is fixed to the header is electrically connected with a master control unit.
In recent years, many protective devices for passengers riding in vehicles have come to be mounted to the vehicles, such as air bag devices or the like which deploy from the steering wheel, the side portions of the seats, and the side portions of the roof; and, in order to answer requirements related to these, various inventions have been proposed in relation to connecting such a protective device for vehicle passengers to a control bus for the vehicle as a whole (for example, refer to Japanese Patent Unexamined Publication No. H10-154992).
Furthermore, in line with this ongoing process of bus connection, inventions have also been proposed related to squibs which are internally fitted with ICs (integrated circuits) for communication and ignition (for example, refer to Japanese Patent 3,294,582).
Furthermore, since a squib is a device which operates a system such as an air bag device or a pre-tensioner device or the like, it is used with the objective of igniting the material which is used for evolving gas. FIGS. 9 and 10 show an example of this type of prior art squib. As shown in these figures, the squib 130 comprises a quantity of explosive 135, which is a so called igniter material and is stored internally, and a header 132; a fine wire (a bridging wire) 131 which is made from a material such as nickel-chrome or platinum is welded to the header 132, and pins 133 and 134 are formed as projecting from the header 132. And an external control unit (not shown in the figures) is connected to these pins 133 and 134 of the squib 130, and, when electrical current is supplied to these pins 133 and 134 from said control unit, the Joule heat generated due to the electrical resistance of the fine bridging wire 131 causes the explosive 135 to be ignited.
Furthermore, in recent years, the number of air bags or pre-tensioners which are fitted to an automobile has had a great tendency to increase. In order to cater for this tendency, as shown in FIG. 11, a technique has been proposed in which a plurality of squibs 140 are connected in parallel upon a pair of wires 142 (a bus connection), and the function of electrical power supply and the function of communication are both simultaneously fulfilled by this two wire bus 142, so that, by performing ignition control by communication commands from a control unit 141, it is possible to dispense with any harness (refer to Japanese Patent Unexamined Publication Nos. H10-154992 and 2000-124932).
In the case of a squib to be utilized with this bus connection, although it is necessary to assemble a communication ignition circuit and a capacitor for ignition to a general purpose type squib according to the prior art, alternatively a squib 140 has been proposed, as shown in FIG. 12, in which a communication ignition circuit 143 and a capacitor for ignition 144 are assembled directly to the squib (refer to Japanese Patent Unexamined Publication No. 2000-241098).
In this case, when a structure is utilized in which a plurality of squibs are connected to a bus, since it is necessary for all of these squibs to be supplied with electrical power from the bus, accordingly it is also necessary for the energy which is required for ignition to be about 1/100 of that required for a general purpose type squib according to the prior art. Due to this, squibs have been proposed which are equipped with ignition elements which can be ignited with low energy (refer to U.S. Pat. Nos. 5,847,309, 5,905,226 and 6,192,802).
As such a type of low energy squib, as shown in FIG. 13, a technique is currently under test in which, by housing a communication circuit, an ignition circuit, and an ignition element within a single package 151, and by housing that package 151 internally within a squib 150 which is formed in the same external shape as a squib according to the prior art, the squib can be directly connected to the bus of the vehicle without making any changes to a passenger restraint device which is already in existence.
Thus, with such a squib which is equipped with an internal IC, there is the beneficial aspect that it is easy to fit it to an inflator device which is already in existence, since, along with the shape of the squib being the same as that of the corresponding prior art component, the ignition element is integrated with the IC.
However, with a structure in which the ignition element is integrated with the IC, since the explosive and the IC are both housed within the cap, it is desirable to provide some type of construction for protecting the ignition element and the IC from gas which is emitted from the explosive over time.
The present invention has been conceived in the light of the above problem, and one of its objects is to provide a squib which, while maintaining its function as a squib, also protects the ignition element and IC from gas which is emitted by the explosive.
Furthermore, in the case of a low energy squib, it is necessary to house the communication and ignition circuit within the header, and moreover it is also necessary to form the ignition element within the ignition circuit. Due to this, it is necessary to preserve a certain empty space within the structure of the header, and accordingly the problem arises that the burden of work when processing the header is increased, and accordingly the cost is increased. Furthermore, since the external shape of this squib is required to be the same as that of a prior art general purpose type squib, it is also necessary to make the communication and ignition circuit package as compact as possible, and accordingly the problem arises that the level of difficulty becomes very great when housing the capacitor for ignition in this package. Yet further, in order to be able to anticipate increased reliability for ignition, it is necessary to preserve close contact between the flammable material (the explosive) and the ignition element; but, in order to do so, it becomes necessary to perform the task of pressure packing for pressing the flammable material into place, and the problem arises that, due to the shape of the circuit package, the work involved cannot be performed without an additional separate process.
Accordingly, the present invention has been conceived in the light of the above problem as well, and another of its objectives is to provide, as a means for solving the above described problems, a low energy squib which, while lowering the work burden, reducing the cost, and providing more reliable ignition, does not require addition of any changes to currently existing restraint devices for persons riding in a vehicle, and which can be connected to the bus.